Heide Knight

You encounter your first Heide Knight early on in the game in The Forest of Fallen Giants. He is sitting, slouched against a tree. He holds a Heide Sword, a valuable weapon at this stage of the game. After engaging the Heide Knight, the main thing to keep in mind is to choose wisely when to strike. He can lash out with some very quick, unsuspecting attacks. For melee fighters, if you keep your shield up you can tightly circle the white knight, blocking his attacks. Keep your eye on your stamina and roll away if you have to. Circling him like this will present you with oporunites to back stab him which, with a few backstabs, makes this fight much quiker and easier. If you miss the backstab nevermind, at least you will have (hopefully) dealt him a flesh-wound. If you are in need of heeling, use the Tree in the centre of the area to put some distance between you and the knight. If you carefully chip away at him, he shouldn't be too hard to dispatch. He is a predictable enemy after a few tries.

alternatively, you can press on until the next bonfire where you can find 5 witching urns on a body to the left of the door leading to the chamber with the bonfire, 4 or 5 withching urns will kill him (confirmed 3 times on first playthrough on PS3)